Preparation

In a small saucepan bring broth to a boil and add onion. Remove pan from heat and steep mixture 10 minutes. Pour liquid through a sieve into a blender and discard onion. Add yolk, mustard, salt, pepper, Worcestershire sauce, and vinegar and blend until smooth. With motor running, add oil in a slow stream, blending until emulsified. Crumble Stilton. With motor off add Stilton, and blend until very smooth. Pour dressing through a sieve into a bowl. Dressing keeps, covered and chilled, 1 week.